1. Field of the Invention
The invention relates in general to speed pattern generators, and more specifically to new and improved terminal slowdown speed pattern generators for elevator systems.
2. Description of the Prior Art
Elevator systems employ a redundant, independent means for detecting an overspeed condition of an elevator car as it approaches a terminal floor. If a first overspeed condition is detected, an auxiliary terminal slowdown speed pattern is generated which is substituted for the normal slowdown speed pattern. If this action fails to slow down the car properly, an emergency terminal stop is initiated. The present invention concerns the development of the auxiliary terminal slowdown speed pattern.
One prior art arrangement utilizes a cam driven distance sensor located on the elevator car to generate the auxiliary terminal speed pattern as it is actuated by a cam in the hoistway. Since the deflection of the distance sensor's arm is small compared with the distance required to slow down the elevator car, it is often necessary to resort to two cams and two sensors in high speed elevator systems.
An improved arrangement for developing an auxiliary terminal slowdown speed pattern is disclosed in U.S. Pat. No. 3,779,346, which is assigned to the same assignee as the present application. In this patent, the terminal slowdown control includes spaced indicia or markers, such as may be provided by a notched blade, and a detector. The markers and detector are mounted such that there is relative movement between them as the elevator car approaches a terminal floor. The notched blade is preferably mounted in the hoistway, and the detector is preferably mounted on the elevator car such that it is aligned with the blade and will detect the spaced teeth on the blade as it passes them.
The markers or teeth on the blade are spaced to provide the desired speed profile for bringing the elevator car to a stop at the associated terminal floor. They are spaced successively closer together in the direction of the terminal, such that the time required for the elevator car to pass between any adjacent pair will be a predetermined constant if the deceleration rate of the car is constant, and at the desired magnitude. If the time elapsed between adjacent pairs is shorter than a predetermined value, monitoring means, including means for converting the elapsed time to a speed error signal, will detect the overspeed and initiate slowdown, i.e., the switching from the usual speed pattern to an auxiliary speed pattern.
The spaced markers, and detector, along with the means for converting the elapsed time between the spaced markers to a speed error signal used for the monitoring function, are also used to generate the auxiliary speed pattern. The speed error signal is summed with a signal responsive to the speed of the elevator car, such as a signal from a tachometer responsive to the elevator drive motor, to provide the required slowdown speed pattern profile.
While this arrangement provides an excellent auxiliary terminal slowdown speed pattern, the speed error signal is limited in the amount of correction it can apply to the signal responsive to car speed. In other words, the auxiliary terminal slowdown speed pattern signal provided by this arrangement is not a full range signal, and will provide the correct speed pattern only as long as the car speed is reducing within the range of correction of the speed error signal. If the car speed is outside this correctable range, an emergency terminal stop will be triggered. It would be desirable to provide a new and improved terminal slowdown speed pattern generator which provides a full range signal, enabling the correct auxiliary terminal slowdown speed pattern to be generated regardless of car speed. A full range signal will also have the advantage of being usable in a pattern clamp arrangement, such as disclosed in U.S. Pat. No. 4,161,235 and co-pending application Ser. No. 356,684, filed Mar. 10, 1982, entitled "Elevator System", which are both assigned to the same assignee as the present application.
The auxiliary terminal slowdown speed pattern of the arrangement disclosed in the subject patent is also generated by primarily analog circuitry utilizing RC circuits for timing. It would also be desirable to provide a new and improved terminal slowdown speed pattern generator which utilizes digital signals whenever possible for accuracy and ease of adjustment, and which does not depend upon RC timing circuits in the critical areas of pattern development.